1. Field of the Invention
This invention relates to an endoscope wherein a face plate-shaped image sensor as a charge coupled device is provided at the forward end portion thereof, and more particularly to an endoscope wherein an article to be observed is displayed on a picture plane of a television for the observation on the basis of image signals obtained through the charge coupled device.
2. Description of the Prior Art
In most cases, the conventional endoscopes have been each constructed such that an objective lens and an eye piece are disposed at opposite end portions of optical fibers for transmitting an image, an image of an article to be observed is made to focus at one end face of the optical fibers and a transmitted image being transmitted through the optical fibers and appearing on the other end face is observed through the eye piece.
While, there has recently been studied a television endoscope utilizing a face plate-shaped image sensor in which a charge transfer device as typified by a charge coupled device is combined with fine light-receiving elements being matrix-arranged. The television endoscope of the type described is advantageous in every respects of that the durability is high, various processings can be applied to electric signals as being image outputs and the use of the endoscope of this type results in a decrease in cost as compared with the conventional endoscope utilizing image guide fibers. In consequence, it has been studied to put the endoscope of this type in the practical use.
Now, the face plate-shaped image sensor used as the charge coupled device arranged at the forward end of the television endoscope has been rendered compact in size due to the improvements in the manufacturing technique and the degree of integration in recent years, however, it cannot be said that the image sensor has been satisfactorily compact in size to be applied to the endoscope. This is because, as well known, the outer diameter of the endoscope should be so small as to be inserted into a cavity in a human body. It is desirable that the outer diameter of a gastric endoscope is about 10 mm or less, for example. Further, even if the image sensor is satisfactorily rendered compact in size, there still is a requirement for the improvements in the resolving power, i.e. an increase in the number of picture elements on the other hand. This requirement may cause the image sensor to be more or less increased in size.
With the above-described circumstances being for a background, in constructing a television endoscope, it becomes an important point how to construct the forward end portion of the endoscope, i.e. how to efficiently arrange the image sensor and the objective optical system for making an optical image be made to focus at the image sensor within a limited space. As a typical construction of the forward end portion of a direct vision endoscope, which has been under study, there is such one in which a face plate-shaped image sensor is disposed on a plane perpendicularly intersecting the longitudinal direction of the end scope and an optical image from a direct vision objective optical system is made to focus at the image sensor as it is. As a typical construction of the forward end portion of a side vision endoscope, which has also been under study, there is such one in which the image sensor is disposed along the longitudinal direction and close to one side wall surface of the endoscope and an optical image from a side vision objective optical system is made to focus at the image sensor. However, when the image sensors are practically assembled into the forward end constructions of the two types described above, there may occur problems. Namely, with the former, when the cross section of the forward end portion is considered, most of the cross sectional area is occupied by the face plate of the image sensor, whereby it becomes very difficult to provide members other than the face plate such for example as a light guide channel, a forceps channel and an air-supply and water-supply channel. Whereas, with the latter, the face plate of the image sensor is disposed close to one side of the endoscope and the optical image from the side vision objective optical system provided at the other side is made to focus at the face plate of the image sensor, whereby, when consideration is given to the cross section of the forward end portion, most of the cross sectional area is occupied by the side vision objective optical system, and moreover, the face plate of the image sensor is disposed close to one side wall of the endoscope, the cross section of which is preferably of a substantially circular shape, so that the cross section of the endoscope may be expected to be deformed to a considerable extent.